1. Field of the Invention
This invention relates to telecommunication networks. More particularly, the invention concerns the control of voice calls in an ATM network.
2. Description of the Prior Art
By way of background, ATM (Asynchronous Transfer Mode) packet networks are now being used to provide bearer pathways for voice communications. In these systems, voice calls between communicating parties are placed on through-connections established by ATM network switching nodes. Such connections are generally under the control of the parties' subscriber equipment, whose call state (on-hook or off-hook) determines connection status (setup, release, etc.).
What is lacking in conventional VoATM (Voice over ATM) systems is an interface for implementing bearer path connection control and manipulation at network points of entry or within the network. In particular, there is no mechanism for positive enforcement of bearer connection establishment and teardown. Connections cannot be terminated except by one or both of the communicating parties. This means that the parties might continue to talk even though billing for a call has stopped (i.e., because the bearer path remains open). Conversely, billing might continue after the parties have ended the call.
Conventional VoATM systems also lack ability to provide pivot points for VoATM lines and trunks carrying ATM bearer traffic into and out of an ATM backbone network. Such pivot points are currently only provided by LAGs (Line Access Gateways) and TAGs (Trunk Access Gateways) that interwork between TDM bearer traffic and packet-oriented (e.g., ATM, IP) bearer traffic. Without a pivot point on the trunk side of an ATM entry point of a switching node, the switching node needs to be aware of when another switching node in a call manipulates the bearer path. The bearer path thereby becomes a shared resource that all switching nodes jointly use to provide their own services. This greatly increases the complexity of implementing services because feature interactions cross switch boundaries. Without a pivot point on the line side of an ATM network entry point, the switching node cannot perform call redirection and insert/remove service circuits in established connections to provide the usual features available to traditional TDM (Time Division Multiplexing) calls. Such services include N-way bridging, announcement playback, tone generation, tone detection, speech recognition, and multicasting.
In addition to the foregoing disadvantages of conventional VoATM systems, certain law enforcement statutes, such as the Communications Assistance for Law Enforcement Act (CALEA) (47 U.S.C. 1001 et seq.), require that a call involving a surveillance subject remain under surveillance even after the subject is no longer a participant in the call. Because court orders for CALEA surveillance may limit the geographic scope over which the surveillance may be performed, there is a need to ensure that the bearer path for a call stays within the geographic bounds within which it may be surveilled. If calling parties are able to establish a bearer path using conventional ATM connections, there is no such guarantee.
Accordingly, there is a need in an ATM network providing VoATM service for an interface system that implements bearer path connection control and manipulation at ATM points of entry of a switching node. The same capability is also needed when data and video calls are transported over ATM.